This invention relates to the synthesis of a class of pharmaceuticals of which N-[1-(s)-Ethoxycarbonyl-3-phenylpropyl]-L-alanyl]-L-proline maleate salt (sold under the trade name Enalapril) is representative; such drugs are useful in inhibiting angiotensin converting enzyme in mammals, especially humans.
These pharmaceuticals are commonly synthesized from an intermediate which has the formula ##STR2## where R.sub.1 is an identifying group of an amino acid (D- or L-; e.g., R.sub.1 is H in the case of glycine and CH.sub.3 in the case of alanine); R.sub.2 is H, alkyl (preferably lower (1-5 carbon atoms, inclusive)), or aralkyl, preferably having 6-8 carbon atoms, inclusive (e.g., benzyl); R.sub.3 is alkoxy (preferably having 1-5 carbon atoms, inclusive, e.g., ethoxy); and n is 0-5, inclusive, most preferably 0-2, inclusive.